1. Field of the Invention
The present invention relates to a calibration method and sports equipment, and more particularly, to a calibration method and sports equipment calibrating a high gravity accelerometer in reference to a low gravity accelerometer.
2. Description of the Prior Art
With advances in Microelectromechanical systems (MEMS), sports equipments are embedded with various kinds of accelerometers or G-sensors to record usage data for athletes. The recorded data can be utilized for analyzing athletic skills. For example, baseball bats and golf clubs are embedded with the accelerometers to record data of bat (or club) swing traces. These data are analyzed by computers to simulate the swing traces on display monitors. As a result, the athletes can repeatedly examine their own swing traces to improve athletic skills.
Please refer to FIG. 1, which is a schematic diagram of a simulated golf swing trace 10 of the prior art. In order to simulate the swing trace 10, acceleration data recorded by accelerometers embedded in a head 110 of a golf club 100 are required. Note that, the accelerations of the head 110 during swing and collision are significantly different due to Golf characteristics. Therefore, both low gravity and high gravity accelerometers are installed in the head 110. The low gravity and high gravity accelerometers are classified based on their top measurement limits. For example, the top measurement limits of the low gravity accelerometers are two, four or eight times gravity. On the other hand, the top measurement limits of the high gravity accelerometers can reach 100, 200 or 400 times gravity.
Generally, a typical measurement error of the accelerometers 1%, which means that a measurement error of an 8 G accelerometer is 0.08 G (G=9.8 m/s2), which is tolerable inmost applications. However, a measurement error of a 400 G accelerometer can reach 4 G, which would result in a serious simulation error for swing trace reconstruction.
Therefore, the industry focuses on reducing the measurement error by calibrating the high gravity accelerometers.